Biology-Cells, Organs & Populations

Animal cells:

• Nucleus- Contains genetic material.
• Cytoplasm- Where most chemical reactions happen, contains enzymes.
• Cell membrane- Holds the cell together, controls what goes in & out.
• Mitochondria- Where respiration takes place, respiration releases energy.
• Ribosomes- Where proteins are made.

Plant cells: (includes all parts of an animal cell)

• Cell wall- Made of cellulose, supports the cell & strengthens it.
• Permanent vacuole- Contains cell sap.
• Chloroplasts- Where photosynthesis occurs, contains chlorophyll.

Diffusion- The spreading out of particles from an area of high concentration to an area of low concentration.

Diffusion happens in both solutions & gases, because the particles are free to move in these sustances. 

The bigger the difference in concentration, the faster the diffusion rate.

Cell membranes

Only very small molecules can diffuse through cell membranes.

E.g. Oxygen, glucose, amino acids & water.

Palisade Leaf Cells- Adapted for photosynthesis

• Packed with chloroplasts- crammed at top of cell, nearer to light.
• Tall shape- lot of surface area exposed, absorbs CO2.
• Thin shape- can pack loads of the cells at top of a leaf.

Guard Cells- Adapted to open & close pores

• Kidney shape- opens & closes the stomata (pores) in a leaf.
• When plant has lots of water, guard cells fill with it & go plump & turgid- this makes stomata open so gases can be exchanged for photosythesis.
• When plant is short of water, guard cells lose water & become flaccid- this makes stomata close, this helpsto stop too much water vapour escaping.
• Thin outer walls & thickened inner walls- makes opening & closing work.
• Sensitive to light- close at night, this saves water.

Red Blood Cells- Adapted to carry oxygen

• Concave shape- big surface area, for absorbing oxygen. Also helps them pass smoothly through capillaries.
• Packed with haemoglobin- pigment that absorbs oxygen.
• No nucleus- leaves more room for haemoglobin

Sperm & Egg Cells- Specialised for reproduction

• Main functions of egg cell- to carry female DNA & to nourish developing embryo. Egg cell also contains huge food reserves to feed embryo.
• When sperm fuses with the egg, the egg's membrane instantly changes it's structure to stop any more sperm. This makes sure offspring end up with right amount of DNA.
• Function of sperm- to get male DNA to female DNA.
• Long tail & streamlined head- helps it swim to the egg.
• Lots of mitochondria- provides energy needed.

• Differentiation- The process by which cells become specialised for a particular job.
• This occurs during development of multicellular organisms.
• Specialised cells>Tissues>Organs>Organ systems

Tissues

Examples of tissues in mammals:

• Muscular tissue- contracts to move what it's attached to.
• Glandular tissue- makes & secretes chemicals like enzymes & hormones.
• Epithelial tissue- covers some parts of the body e.g. the inside of the gut.

Plant Tissues

• Mesophyll tissue- where photosythesis in a plant occurs.
• Xylem & phloem- they transport things like water, mineral ions & sucrose around the plant.
• Epidermal tissue- covers the whole plant.

Equation for photosynthesis

Carbon Dioxide + Water ----> Glucose + Oxygen

CO2 + H2O ----> C6H12O6 + O2 

Limiting Factors

• Light
• Temperature
• Amount of CO2

Light

Not enough light slows down photosynthesis.

• Light provides energy needed for photosynthesis.
• As light level is raised, rate of photosynthesis increases steadily up to a certain point.

Carbon Dioxide

CO2 is one of the raw materials needed for photosynthesis.

• As with the light intensity, amount of CO2 will only increase rate of photosynthesis up to a certain point.
• After this, the graph flattens out showing that CO2 is no longer the limiting factor.

Temperature

• If temp is the limiting factor, it's too low. Enzymes needed for photosynthesis work more slowly at low temps.
• If the plant gets too hot, enzymes needed could be destroyed or denatured.
• This happens at 45°C.

For Respiration:

• Plants manufacture glucose in their leaves.
• Some is used for respiration.
• This releases energy which enables them to convert the rest of the glucose into various other useful substances, this can be used to build new cells & grow.

Making Cell Walls:

• Glucose is converted into cellulose for making strong cell walls.

Making Proteins:

• Glucose is combined with nitrate ions to make amino acids, which are then made into proteins.

Stored In Seeds:

• Glucose is turned into lipids (fats & oils) for storing in seeds. 
• Seeds also store starch.

Stored As Starch:

• Glucose is turned into starch & stored in roots, stems & leaves, for winter.
• Starch is insoluble which makes it better for storing than glucose- if a cell has lots of glucose, it draws in loads of water & swells up.
• Potatoe & parsnip plants store a lot of starch underground. 

Environment:

• A habitat is where an organism lives.
  
• The distribution of an organism is where the organism is found.

Environmental factors:

• Temperature
  
• Availability of water
• Availability of oxygen & carbon dioxide
• Availability of nutrients
• Amount of light

Using Quadrats:

• Place quadrat at a random point on the ground.
• Count all organisms within the quadrat.
• Repeat as many times as you can.
• Work out mean number of organisms per quadrat.
• Mean- TOTAL number of organisms ÷ NUMBER of quadrats